The present invention relates to an information carrying medium such as IC card and the like used in cash dispensing bank terminals, POS (Point of Sales) and other equipment. More particularly, the invention is concerned with an information protecting method which is effective for protecting secret information as the well as information medium against defraudation.
The security of secrecy in the information carrying medium such as an IC card or the like is ensured mainly by resorting to the use of personal identification number (hereinafter referred to as PIN) in the present state of the art. Of course, it is also known to encode the contents recoded in the medium in an effort to make difficult the read-out of the contents. However, in consideration of the fact that defrauders' technique for attempting to make access to the secret information has been considerably enhanced recently, much difficulty is encountered in taking the more positive and secure measures for protecting the information against defraudation.
By way of example, Japanese Patent Laid-Open Publication No. 60-198683 discloses an IC card system in which a random access memory (RAM) is incorporated in the IC card for storing a time limit within which the information entered in the IC card can be read out and the transaction using the IC card is validated.
In the case of the prior known IC card system mentioned above, the data can be read out from the IC card by means of a card reader/writer device. As a result, there exists still a possibility that the contents of the card might be read out through suitable means for the bad-will purpose such as illegal alteration of the valid term, presenting a problem remaining not yet solved.